The 24-year-old served an eight-month deployment in Iraq in 2008 and was discharged in 2010. According to secret grand jury testimony, Ocampo reportedly joined the Marine Corps because "he needed to kill." Ocampo said he was disappointed when he did not see any combat during a tour of duty because he became a truck driver instead of a killer, court documents state.

Ocampo has pleaded not guilty to all charges. His trial is scheduled for Sept. 10.

The homeless murders took place in Orange County over a three-week period starting in December 2011. Ocampo was arrested following the stabbing death of the fourth homeless man outside a Carl's Jr. restaurant in Anaheim on Jan. 13.

Ocampo is also charged with stabbing to death a mother and son in Yorba Linda last October. Unlike the homeless victims, authorities allege Ocampo knew 53-year-old Raquel Estrada and her 34-year-old son Juan Herrera through Estrada's younger son.